4 research outputs found
Nature of Valence Transition and Spin Moment in Ag<sub><i>n</i></sub>V<sup>+</sup> Clusters
Evolution in the atomic structure,
bonding characteristics, stability,
and the spin magnetic moment of neutral and cationic Ag<sub><i>n</i></sub>V clusters has been investigated using first-principles
density functional approach with gradient corrected functional. It
is shown that at small sizes, the V 4s states hybridize with Ag states
to form 1S and 1P like superatomic orbitals, whereas the 3d states
are localized on V giving the V atom an effective valence of 1 or
2. Starting from Ag<sub>8</sub>V<sup>+</sup>, the V 3d states begin
to participate in the bonding by hybridizing with the nearly free
electron gas to form 1D superatomic orbitals increasing the V atom
effective valence toward 5. For the cationic clusters, this changing
valence results in three shell closures that lead to stable species.
These occur for cationic clusters containing 5, 7, and 14 Ag atoms.
The first two stable species correspond to filled 1S and 1P shells
in two and three dimensions with a valence of 2 for V, whereas the
closure at 14 Ag atoms correspond to filled 1S, 1P, and 1D shells
with V site exhibiting a valence of 5. The transition from filled
1S and 1P shells to filled 1S, 1P, and 1D shells is confirmed by a
quenching of the spin magnetic moment. The theoretical findings are
consistent with the observed drops in intensity in the mass spectrum
of Ag<sub><i>n</i></sub>V<sup>+</sup> clusters after 5,
7, and 14 Ag atoms
Efficient Calculation of the Rotational <b>g</b> Tensor from Auxiliary Density Functional Theory
The computation of the rotational <b>g</b> tensor with the
recently developed auxiliary density functional theory (ADFT) gauge
including atomic orbital (GIAO) methodology is presented. For the
rotational <b>g</b> tensor, the calculation of the magnetizability
tensor represents the most demanding computational task. With the
ADFT-GIAO methodology, the CPU time for the magnetizability tensor
calculation can be dramatically reduced. Therefore, it seems most
desirable to employ the ADFT-GIAO methodology also for the computation
of the rotational <b>g</b> tensor. In this work, the quality
of rotational <b>g</b> tensors obtained with the ADFT-GIAO methodology
is compared with available experimental data as well as with other
theoretical results at the HartreeāFock and coupled-cluster
level of theory. It is found that the agreement between the ADFT-GIAO
results and the experiment is good. Furthermore, we also show that
the ADFT-GIAO <b>g</b> tensor calculation is applicable to large
systems like carbon nanotube models containing hundreds of atom and
thousands of basis functions
Evolution of the Spin Magnetic Moments and Atomic Valence of Vanadium in VCu<sub><i>x</i></sub><sup>+</sup>, VAg<sub><i>x</i></sub><sup>+</sup>, and VAu<sub><i>x</i></sub><sup>+</sup> Clusters (<i>x</i> = 3ā14)
The
atomic structures, bonding characteristics, spin magnetic moments,
and stability of VCu<sub><i>x</i></sub><sup>+</sup>, VAg<sub><i>x</i></sub><sup>+</sup>, and VAu<sub><i>x</i></sub><sup>+</sup> (<i>x</i> = 3ā14) clusters were
examined using density functional theory. Our studies indicate that
the effective valence of vanadium is size-dependent and that at small
sizes some of the valence electrons of vanadium are localized on vanadium,
while at larger sizes the 3d orbitals of the vanadium participate
in metallic bonding eventually quenching the spin magnetic moment.
The electronic stability of the clusters may be understood through
a split-shell model that partitions the valence electrons in either
a delocalized shell or localized on the vanadium atom. A molecular
orbital analysis reveals that in planar clusters the delocalization
of the 3d orbital of vanadium is enhanced when surrounded by gold
due to enhanced 6s-5d hybridization. Once the clusters become three-dimensional,
this hybridization is reduced, and copper most readily delocalizes
the vanadiumās valence electrons. By understanding these unique
features, greater insight is offered into the role of a host materialās
electronic structure in determining the bonding characteristics and
stability of localized spin magnetic moments in quantum confined systems